Snakehead Fish: Invasive Predators in North America
What Is a Snakehead?
Snakeheads are predatory fish that have some surprising characteristics. The giant snakehead is a voracious predator with sharp teeth, a large mouth and strong jaws. It's been called a "frankenfish" due to its aggressive reputation. It has a lung-like organ in addition to gills and can breathe in air. The fish is able to survive out of water for several days. It travels over land with a wriggling motion and moves up to a quarter of a mile to reach a new waterway.
Other snakehead species don't seem to be quite as aggressive or as capable of moving on land as the giant snakehead, but they are all fierce and very capable predators and they can all breathe in air.
Snakeheads are native to Asia and Africa but have been transported to North America for the pet trade and for food stores that sell living fish. They have appeared in some U.S. and Canadian waterways, presumably because they were released from home aquariums. Their presence in the wild is very worrying. They have no natural predators in North America and may be a serious threat to native wildlife.
Channa pulcra, the Peacock Snakehead
Fish That Can Breathe in Air
Snakeheads have an elongated body, a long dorsal fin on their back and a long anal fin on their belly. Their head has enlarged scales and their eyes are often shifted towards the front of their head. These features resemble those of a snake, giving the fish their name.
Snakeheads obtains oxygen from air as well as water. The fish use their gills to obtain oxygen from water, just as other fish do. Water enters their mouth and travels to the gills on both sides of the body. Oxygen passes from the water into the gill tissue and then enters blood vessels. The water leaves the gills through the opening behind the operculum (the bony flap that covers each gill chamber).
To breathe in air, the fish use a space in their head above their gills called the suprabranchial chamber or the suprabranchial organ. Air that the fish gulps from the water surface enters the suprabranchial chamber. Here oxygen from the air passes into blood vessels in the tissue lining the chamber.
The suprabranchial chamber of a snakehead is quite similar to the labyrinth organ found in some other air-breathing fish. Examples of labyrinth fish include the Siamese fighting fish, the climbing perch and many types of gouramis.
A Giant Snakehead in an Aquarium
The Giant Snakehead
The giant snakehead (Channa micropeltes) lives in freshwater, like other snakeheads. Living up to its name, it may reach more than 3.3 feet (a meter) in length and weigh over 44 pounds (20 kilograms).
The fish is quite variable in appearance. It has a dark grey, blue-black or black background color with white, silver or blue-green markings. The undersurface of the fish is much lighter in color than the rest of the fish.
The giant snakehead is also known as the red snakehead. This name comes from the color of the young fish, or fry. In some parts of the world fisherman refer to the giant snakehead as a toman. It's a popular prey in sport fishing and is also enjoyed as an edible fish in some countries.
This snakehead has a reputation as a fearsome and even vicious predator. Its diet consists mainly of other fish, but it also eats frogs, crustaceans and even birds. It reportedly kills more animals than it eats.
Giant snakeheads create a nest by clearing a cylindrical area in the middle of aquatic vegetation. When the eggs are laid they rise to the top of the water column and are carefully guarded by the adults. The parents also guard the fry, which helps them to survive.
The Northern Snakehead
Although they are classified in the same genus, the northern snakehead and the giant snakehead look quite different from one another. The northern snakehead is an attractive fish that has a tan, brown, grey or grey-green background color covered with darker blotches and stripes. The body is torpedo-shaped and the top of the head is noticeably flattened. The lower jaw of the fish protrudes beyond its upper jaw.
The northern snakehead is native to China, Korea and Russia and has spread to other areas of Southeast Asia. It lives in areas where the water is muddy and is flowing slowly or is stagnant. It feeds mainly on other fish but also eats crustaceans and insects. Like the giant snakehead, it's often described as "ferocious". The species is an obligate air breather - it must breathe air as well as absorb oxygen through its gills in order to survive.
There is some debate about how capable this fish is at moving over land. There are claims that it can travel on land and survive for three or four days out of water, provided it stays moist, just like a giant snakehead. Many researchers say that it can't move far when it leaves the water and that under normal circumstances it can survive for only a few hours in air, however.
A Northern Snakehead at the National Aquarium
There is still a lot to learn about the life history and reproduction of the northern snakehead. Understanding the fish's habits is essential in order to control its population when it becomes invasive.
In 2007, a northern snakehead nest was discovered in the Potomac river in the United States. The nest was a cylindrical column of water surrounded by an aquatic plant called Hydrilla. A circular mat of Hydrilla formed a canopy or roof on top of the nest. Orange-yellow eggs had been laid on the canopy. The eggs weren't adhesive and were held in place and hidden by the plant leaves and stems. The adults - both the male and the female - patrolled the water underneath the canopy.
Northern snakehead nests have been found in other areas, too. They have all been cylindrical nests surrounded by vegetation and have been about one meter in diameter. These nests have lacked a canopy, however.
The fish have a high fecundity and lay 22,000 to 115,000 eggs at a time. They breed up to five times a year. Although some of the eggs and fry die, parental care likely improves reproductive success compared to the situation in fish that don't guard their young.
Invasion of the Snakeheads
Wild Snakeheads in North America
Wild snakeheads, including giant snakeheads, are sighted periodically in various parts of North America. In at least three areas snakeheads have formed a resident population and are reproducing.
The northern snakehead is found in the Potomac river and its tributaries in the state of Maryland. The bullseye snakehead (Channa marulius) has established itself in part of Florida. The adults of this species frequently have red eyes and a black spot surrounded by orange at the base of their tail fin. The blotched snakehead (Channa maculata) lives in Hawaii and is quite similar in appearance to the northern snakehead.
Snakeheads are thought to have entered the wild when they were released from home aquariums, perhaps when they grew too large or too expensive to keep. They may also have been released into ponds by fish sellers or other people who hoped that the snakeheads would reproduce to produce a convenient and free source of edible fish.
The northern snakehead has established itself firmly in the Potomac River system, with a population estimated at somewhere above 21,000 individuals, ranging through more than 120 river miles (200 kilometers).— National Geographic
A Blotched Snakehead in Burnaby's Central Park
An Invasive Fish in Burnaby, British Columbia
In 2012, a snakehead fish was found living in a park pond in Burnaby, British Columbia. It was caught when the pond was partially drained. There were concerns that the fish was a northern snakehead, which would have been capable of living through a southwestern BC winter. In November 2013, however, the fish was identified as a blotched snakehead. This species would be unlikely to survive through the local winter, which although mild in terms of Canadian winters is much colder than the climate in the snakehead's native habitat. No more wild snakeheads have been discovered in the province since the 2012 discovery, to the relief of many British Columbians, including me.
Central Park: The Temporary Home of an Invasive Fish
Dangers of Invasive Snakehead Populations
The presence of wild snakeheads in North America worries some conservation officers and officials very much. The fish have no natural predators. There is talk of horrible scenarios such as native animal species being wiped out by the fish. Snakeheads may not only prey on native animals but also pass parasites to them.
The presence of any invasive species - especially a predator - must always be taken seriously. Snakeheads definitely have the potential to create an environmental problem. The areas that they have invaded need to be monitored closely. It may only be a matter of time before serious effects are noticed due to the presence of the fish. At the moment, though, it's not clear how much damage snakeheads are causing to their ecosystem and how significant or widespread any damage is.
In Maryland, officials have enlisted the aid of the public in the effort to control the northern snakehead population. They are advertising the tastiness of the snakehead's flesh to encourage fishing and are holding sports fishing competitions.
In general, snakeheads aren't dangerous to humans. The only times they may show aggression towards us is when they're disturbed while they're protecting their eggs or young and when they're caught. There have been reports of quite serious injuries caused by giant snakehead bites in these situations.
The Future for Snakeheads in North America
Single snakehead fish are generally quickly removed by authorities once they're discovered. Once reproduction has occurred and a population has formed, however, removing the fish is difficult or even impossible, especially when the population is distributed over a wide area. As some people have said, the snakeheads in the Potomac River system are likely here to stay,
The outcome of the snakehead presence is unknown. Will the dire predictions of conservationists come true? Will we be able to avoid these consequences if we keep the snakehead population under control? Are we overreacting to the presence of snakeheads, as a few people have suggested, or are they actually as dangerous for the environment as many scientists say? These questions can't be answered yet. It may take years to find the answers, which is why great caution is needed in the present.
© 2013 Linda Crampton